be to = that的说法不知从何而来,感觉不甚可取。
本句关键是抓住what aids there were这个名词性关系从句,它作were immemorial的主语。
what aids there were = The aids that there were,至于to lighten ...不定式可以看作aids的修饰语。
类比:
Whoever wins the game will get a prize. = The person who wins the game will get a prize.